1. Field of the Invention
The invention relates to a system for heart monitoring and a method for heart monitoring. The system comprises an implantable medical device adapted to pick up in intracardiac electrocardiogram and an external device adapted to wirelessly communicate with the implantable medical device. The method includes a step of acquiring an intracardiac electrocardiogram and a step of processing the intracardiac electrocardiogram. More particularly, the invention refers to a system and a method for generating a surface electrocardiogram (SECG) from an intracardiac electrocardiogram (IEGM).
2. Description of the Related Art
During pacemaker or ICD follow-up, a surface ECG (SECG) is routinely measured to examine the status of the electrical conduction system of the heart, and to confirm the normal functionality of the implant device, for instance, to verify pacing capture control and ensure proper arrhythmia detection. However, measuring SECG is associated with several drawbacks. First, it increases the duration of the follow-up time and adds to the overall cost. Second, skin preparation and electrode handling may bring considerable inconvenience to the patient, particularly for the females. Third, from one follow-up session to another, the electrodes may not be placed at the exact same locations on the patient, thus resulting in somewhat different SECG. Fourth, externally attached electrodes are subject to motion artifacts from postural changes and the relative displacement between the skin and the electrodes. Finally, the SECG is known to be susceptible to interference such as muscle noise, power line interference, baseline drift from respiration or motion, etc.
Therefore, there is a need to provide the implant device Lead-Free ECG feature, that is, to provide a means to generate a SECG-like output ECG signal without the need for attaching the skin electrodes to the patients.
One method for Lead-Free ECG is based on subcutaneous electrodes or subcutaneous electrode array (SEA). For example, U.S. Pat. No. 5,331,966 issued to Bennett et al. discloses a method and apparatus for providing SECG-like signals via an array of relatively closely spaced subcutaneous electrodes located on the body of an implanted device. In a typical embodiment, an array of three electrodes disposed orthogonally on the surface of the pulse generator and connector block and facing outwardly towards the patient's skin is employed to develop the far-field IEGM signal comprising the P-QRS-T signals that are similar to the SECG.
Several patents were issued to further improve the design of the SEA. For example, U.S. Pat. No. 6,522,915 discloses an alternate method and apparatus for detecting electrical cardiac signals via a SEA located on a shroud circumferentially placed on the perimeter of an implanted pacemaker. U.S. Pat. No. 6,512,940 by Brabec et al. discloses the use of a spiral electrode using in conjunction with the shroud described in the Ceballos et al. disclosure. In addition, U.S. Pat. Nos. 6,564,106 and 6,631,290, both issued to Guck and Donders, discloses the use of sensing electrodes placed into recesses incorporated along and into the peripheral edge of the implantable pacemaker.
Furthermore, U.S. Pat. No. 6,505,067 issued to Lee et al. discloses a system and method for deriving a virtual SECG based on the signals recorded by the SEA. The SEA comprises at least three (preferably 3 or 4) subcutaneous electrodes located on the surface of the implant device. The signals recorded between these electrodes form independent directional vectors. The method used to determine the virtual SECG is based on vector arithmetic principles.
Although the far-field IEGM recorded by the SEA may approximate the SECG, the disadvantage is the need for special design, fabrication, and manufacture of the SEA and the associated circuits, which add to the hardware complexity.
A different approach for Lead-Free ECG is based on far-field IEGM recorded by existing implant device and their lead system. For example, U.S. Pat. No. 5,265,602 issued to Anderson et al. discloses a pacemaker, which has a special sense configuration that records the IEGM between the RA ring and the RV ring electrodes. The ‘RA ring-RV ring’ far-field IEGM is relatively unaffected by the after-potentials and polarization effects, but its morphology is generally quite different from SECG.
Similar approach is disclosed in U.S. Pat. No. 6,658,283 issued to Bornzin et al. According to this disclosure, far-field IEGM is recorded from various lead configurations between widely spaced electrodes including RA tip, RV tip, RA ring, RV ring, and case (including the ‘RA ring-RV ring’ configuration). The recorded far-field IEGM is further processed by a cascade of linear filters with designed output frequency bands to generate the Lead-Free ECG, which may not be satisfactory in terms of signal amplitude and morphology.
Another approach is disclosed in U.S. Pat. No. 5,740,811 issued to Hedberg et al. This patent also discloses multiple lead configurations for measuring the far-field IEGM. One or more channels of the far-field IEGM are first pre-processed (amplified, filtered, blocked, transferred), then post-processed by a pre-trained artificial neural network or fuzzy logic to generate the Lead-Free ECG. However, the artificial neural network or fuzzy logic trained from one dataset may not be applicable to another dataset.
U.S. Pat. No. 6,813,514 issued to Kroll et al. discloses a method to emulate the multi-lead SECG by solving the forward problem. Each channel of SECG or IEGM is converted into a time-varying vector. The SECG matrix (containing multiple SECG vectors) is linearly linked to the IEGM matrix (containing multiple IEGM vectors) by a transfer matrix, which can be pre-calculated by solving the inverse problem. However, this method requires multi-channel IEGM recordings. Moreover, calibration of different transfer matrices is needed to account for different factors affecting the relative locations of the internal leads, such as respiration and posture.
In view of the forgoing descriptions, the present invention provides an advanced Lead-free ECG method and apparatus. In this disclosure, the following terms are used:
TermDescriptionAEGMAtrial electrogramAPAtrial pace event = effective atrial stimulation pulseArsatrial refractory sense eventASAtrial sense eventAVAtrial-ventricular (or atrioventricular)ICDImplantable cardioverter-defibrillatorIEGMIntracardiac electrogramNLMSNormalized least mean squarePVARPpost ventricular atrial refractory periodRARight atriumRVRight ventricleSEASubcutaneous electrode arraySECGSurface electrocardiogramSVCSuperior vena cavaVEGMVentricular electrogramVPVentricular pace event = effective ventricular stimulation pulseVSVentricular sense event